This invention relates to heating a heat shrinkable material. More particularly it relates to an apparatus and method for heating a heat shrinkable tube positioned over a wire splice. For a wide variety of uses it is necessary to splice wires together. In splicing electrical wires together, portions of the insulating materials, usually rubber, plastic or like material, will have been removed, exposing the bare wires. A favored method of insulating the bare wires is by sliding a length of heat shrinkable tubing over the splice and the bare wire and heating the tubing so that the tubing will shrink. For many applications the tubing will have an inner layer of adhesive which will melt when heated and when removed from the heating source will seal the splice.
One method of heating the tubing has been by blowing a stream of hot air on the tubing through a hand held hot air gun. The hot air gun is bulky and tends to become quite hot. The disadvantages of the hot air gun method are that the gun is slow and poses a danger of burning in the operation due to the temperatures the gun can reach and the tubing is not heated symmetrically and can also burn.
Another method for heating the tubing is by the heating apparatus described in U.S. Pat. No. 3,515,853, wherein a heating device includes two aligned semi-cylindrical sides which, when closed, form a cylindrical structure that encircles the tubing to be heated. Each side has a plurality of spaced incandescent filaments which provide the heat.
Other methods for heating the tubing would include a toaster and a conveyor belt heater. The toaster would operate similar to a household toaster where the toaster would be constructed without the side panels and the wire assembly, comprising the at least one first wire spliced to the at least one second wire, with the heat shrinkable tube covering the splice, would be placed in the toaster thus activating the heating mechanism in the toaster which would consist of radiant heaters, and a timing device in the toaster would then pop the wire assembly up similar to toast popping up in a household toaster. In the conveyor belt arrangement the wire assembly would be laid on the conveyor belt and the conveyor belt would run the wire assembly through a heater and then out of the heater thus heat shrinking the tubing.
One important use of wire-splicing is in the manufacture of wire harnesses for automobiles. In making the wire harness a plurality of splices, connecting one or more first wires to one or more second wires, are made throughout the harness. The splices are typically made by welding, preferably by ultrasonic welding, and the splice is usually insulated by heat shrinkable tubing often having an inner adhesive layer.
Typically it takes an operator approximately seven seconds for the welding operation when welding one first wire to one second wire. As the number of first wires and the number of second wires increase, the length of time to complete the weld increases. It would be desirable for an operator performing the welding operation to also insulate the weld or the splice without substantially adding to the time required to complete the welding or splicing operation. It would also be desirable for any splice insulating operation to occupy the least possible amount of space. Any operation that occupied excessive space as would a typical conveyor belt arrangement, would make it awkward for the operator to both complete the welding operation and the insulating operation. For at least one commercially available ultrasonic welder the available space would be for a piece of equipment that was less than about 15 cm (6 inches) wide and about 15 cm (6 inches) high and less than about 50 cm long.